The present invention relates to a terminal structure for a resin-sealed semiconductor device, such as a diode, thyristor or transistor module.
FIGS. 9(a)-9(c) and 10 show a conventional resin-sealed semiconductor device and the related terminal structure. In the figures, the semiconductor device includes a heat dissipating metal base (1), an insulation substrate (2), a semiconductor chip (3), an externally drawn terminal (4), an outer casing (5) made of resin, sealing module resin (6), such as epoxy resin, for filling in the casing, and a terminal nut (7) mounted in a recess on top of the outer casing (5).
The semiconductor device with such a structure is assembled in the following manner. First, the semiconductor chip (3) and the externally drawn terminal (4) which is not yet bent at this time are mounted on the metal base (1) to assemble a circuit assembly. Then, the outer casing (5) is placed via the insulating substrate (2) on the circuit assembly, which is bonded with the metal base (1), and filled with the molding resin (6) injected through a resin injection hole opened at the top of the outer casing (5), which is then hardened to seal the circuit assembly.
Thereafter, the terminal nut (7) is mounted on a recess (5a), which is a polygonal hole corresponding to the outer dimension of the terminal nut and formed on top of the outer casing (5), and a top portion of the externally drawn terminal (4) drawn out through the outer casing (5) is bent into an L shape from a straight state indicated by the chain lines in FIG. 10 to a position shown by solid lines, while an external wire connecting portion (4a) is superimposed on the terminal nut (7). Numeral (4b) is a hole drilled on the external wire connecting portion (4a) where a fixing screw is inserted.
The conventional terminal structure described above has the following problems because of a lack of mechanical strength of the semiconductor used.
That is, the externally drawn terminal with the external wire connecting portion on its tip drawn outwards from the outer casing through the molded resin layer in the casing is only supported by a single point. In case the large tensile external force shown by arrow F is imposed on an external wiring (8) when a connecting terminal metal part (9) of the external wiring (8) has been tightened by a screw (10) onto the external wire connecting portion (4a) as shown in FIG. 11, the tip of the externally drawn terminal (4) that has been bent into the L shape is pulled in a direction (P) and is deformed as shown, so that the terminal may be pulled out with the nut (7) from the outer casing (5) and floated upward.
Moreover, if a repeated load, such as vibration, is imposed on the semiconductor device for a long period of time while such a deformation is made on the externally drawn terminal (4), stress will be concentrated on the bent part of the externally drawn terminal (4) embedded in the module resin inside the outer casing and protruding outside the casing.
As a result, a breakage of the externally drawn terminal may happen at the bent part because of elastic fatigue, which can lead to a serious failure of the semiconductor device as it becomes impossible to energize the device.
The present invention has been made after considering these problems, with the intention of solving the problems on the externally drawn terminal of the resin-sealed semiconductor device described earlier, and provides a terminal structure for a resin-sealed semiconductor device with improved support strength against external force at the externally drawn terminal.